Optical sorting and detection of sub-micron objects in a motional standing wave

An extended interference pattern close to surface may result in both a transmissive or evanescent surface fields for large area manipulation of trapped particles. The affinity of differing particle sizes to a moving standing wave light pattern allows us to hold and deliver them in a bi-directional manner and importantly demonstrate experimentally particle sorting in the sub-micron region. This is performed without the need of fluid flow (static sorting). Theoretical calculations experimentally confirm that certain sizes of colloidal particles thermally hop more easily between neighboring traps. A new generic method is also presented for particle position detection in an extended periodic light pattern and applied to characterization of optical traps and particle behaviorComment: 5 pages, 6 figures, Optical Trapping pape

Non-diffracting beam synthesis used for optical trapping and delivery of sub-micron objects

ABSTRACT We demonstrate the use of interference between non-diffracting Bessel beams (BB) to generate a system of optical traps. They offer sub-micron particle confinement, delivery and organization over a distance of hundreds of µm. We analyze system of two identical counter-propagating BBs and the case of two co-propagating BBs with different propagation constants separately. In both of these cases, the interference results in periodic on-axis intensity oscillations involving particle confinement. Altering the phase of one of the interfering beams, the whole structure of optical traps can be shifted axially. Implementing this conveyor belt enables the particle delivery over the whole distance where the optical traps are strong enough for particle confinement. Experimentally we succeeded with generation of both of these systems. In case of two counter-propagating BBs we observed a strong sub-micron particle confinement, while in case of co-propagating BBs the confinement was observed only with help of fluid flow against the radiation pressure of both beams

Optically Anisotropic Colloids of Controllable Shape

Solid spheres, disks, and ellipsoids with micrometer-scale bipolar anisotropic character respond to external electric fields by aligning their mean optical axes parallel to the field. The monodisperse, optically anisotropic colloids (see Figure) are synthesized by photopolymerization of a monodisperse liquid-crystal emulsion after mechanical deformation of the drops.</p

Passive optical separation within a 'nondiffracting' light beam

A passive, optical cell sorter is created using the light pattern of a 'nondiffracting' beam - the Bessel beam. As a precursor to cell sorting studies, microspheres are used to test the resolution of the sorter on the basis of particle size and refractive index. Variations in size and, more noticeably, refractive index, lead to a marked difference in the migration time of spheres in the Bessel beam. Intrinsic differences (size, refractive index) between native (unlabeled) cell populations are utilized for cell sorting. The large difference in size between erythrocytes and lymphocytes results in their successful separation in this beam pattern. The intrinsic differences in size and refractive index of other cells in the study (HL60 human promyelocytic leukaemic cells, murine bone marrow, and murine stem/progenitor cells) are not large enough to induce passive optical separation. Silica microsphere tags are attached to cells of interest to modify their size and refractive index, resulting in the separation of labeled cells. Cells collected after separation are viable, as evidenced by trypan blue dye exclusion, their ability to clone in vitro, continued growth in culture, and lack of expression of Caspase 3, a marker of apoptosis. (C) 2007 Society of Photo-Optical Instrumentation Engineers.</p

Method and Experimental Study of Zeolite Crystal Manipulation Based in Hydrodynamic Forces for Single Crystal Assessment

In this work, we report an optofluidic system for manipulation of orientation of zeolite crystals near the bottom of a rectangular cross-sectional, straight, quartz microfluidic channel. Manipulation is accomplished by using two computer-controlled syringe pumps that generate adequate hydrodynamic forces for translation and rotation of crystals. Rotation of a crystal around its longitudinal axis allows us to inspect its four major faces for defects. Coffin-shaped zeolite crystals have been studied by several authors by fixing them to a substrate, using two different crystals to assess the roof and gable orientations. The proposed system permits complete assessment of a single crystal by shifting it between roof and gable orientations; moreover the medium can be controlled. Computational fluid dynamics simulations show that crystals in free motion near the bottom of the channel should move faster than the velocity estimated from video. An opposing force, which prevents the crystals from moving freely, has been calculated in order to match translation velocities from simulations and experiments for three given flow rates. The reported optofluidic system is proposed as a novel tool that we believe will open new possibilities for individual zeolite crystal assessment by manipulation of its orientation and medium control